Writing Chemical Equations

Writing Chemical Writing Chemical EquationsEquations

Parts of a ReactionParts of a Reaction

►ReactantsReactants The starting materials in a chemical The starting materials in a chemical

reactionreaction

►ProductsProducts The substances that are formed in a The substances that are formed in a

chemical reactionchemical reaction

Parts of a ReactionParts of a Reaction

►A A chemical equationchemical equation shows how shows how atoms are rearranged during a reactionatoms are rearranged during a reaction Reactants appear on the LEFTReactants appear on the LEFT Products appear on the RIGHTProducts appear on the RIGHT An arrow separates the reactants from the An arrow separates the reactants from the

products (products ())

Reactants Reactants Products Products

Special NotationsSpecial Notations

►Descriptions of the compounds appear as subscripts after the compound.

►Gas: (g)

►Liquid: (l)

►Solid: (s)

►Aqueous: Dissolved in water (aq)

Special NotationsSpecial Notations

►Special conditions appear with the arrow.

►Heat: Heat is added to make the reaction happen

►Catalyst: A catalyst is added in order for the reaction to happen – The compound is listed Pt

Writing a Chemical EquationWriting a Chemical Equation

Potassium oxide (KPotassium oxide (K22O) and water react O) and water react to form potassium hydroxide (KOH).to form potassium hydroxide (KOH).

Reactants: KReactants: K22O, HO, H22OO Products: KOHProducts: KOH

KK22O + HO + H22O O KOH KOH


Aluminum and iron oxide (FeO) react to Aluminum and iron oxide (FeO) react to form aluminum oxide (Alform aluminum oxide (Al22OO33) and iron.) and iron.

Reactants: Al, FeOReactants: Al, FeO Products: AlProducts: Al22OO33, Fe, Fe

Al + FeO Al + FeO Al Al22OO33 + Fe + Fe


Silicon dioxide (SiOSilicon dioxide (SiO22) and hydrogen ) and hydrogen fluoride (HF) react to form silicon fluoride (HF) react to form silicon tetrafluoride (SiFtetrafluoride (SiF44) and water.) and water.

Reactants: SiOReactants: SiO22, HF, HF

Products: SiFProducts: SiF44, H, H22OO

SiOSiO22 + HF + HF SiF SiF44 + H + H22OO


Solid sodium carbonate (NaSolid sodium carbonate (Na22COCO33) and ) and aqueous hydrochloric acid (HCl) react to aqueous hydrochloric acid (HCl) react to form carbon dioxide gas (COform carbon dioxide gas (CO22), liquid ), liquid water, and aqueous sodium chloride (NaCl)water, and aqueous sodium chloride (NaCl)

Reactants: NaReactants: Na22COCO3(s)3(s), HCl, HCl(aq)(aq)

Products: COProducts: CO2(g)2(g), H, H22OO((ll)), NaCl, NaCl(aq)(aq)

NaNa22COCO3(s)3(s) + HCl + HCl(aq)(aq) CO CO2(g)2(g) + H + H22OO((ll)) + NaCl + NaCl(aq)(aq)


Heating solid sodium nitrate (NaNOHeating solid sodium nitrate (NaNO33) ) results in solid sodium nitrite (NaNOresults in solid sodium nitrite (NaNO22) ) and gaseous oxygen (Oand gaseous oxygen (O22))

Reactants: NaNOReactants: NaNO3(s)3(s)

Products: NaNOProducts: NaNO2(s)2(s), O, O2(g)2(g)

Special Conditions: HeatSpecial Conditions: Heat

NaNONaNO3(s)3(s) NaNONaNO2(s)2(s) + O + O2(g)2(g)


Aqueous hydrogen peroxide (HAqueous hydrogen peroxide (H22OO22) reacts to ) reacts to form liquid water (Hform liquid water (H22O) and oxygen gas (OO) and oxygen gas (O22) ) in the presence of a platinum catalyst (Pt).in the presence of a platinum catalyst (Pt).

Reactants: HReactants: H22OO2(aq)2(aq)

Products: HProducts: H22O O ((ll)), O, O2(g)2(g)

Special Conditions: Platinum CatalystSpecial Conditions: Platinum Catalyst

HH22OO2(aq)2(aq) HH22O O ((ll))+ O+ O2(g)2(g) Pt

Balancing an EquationBalancing an Equation

► In a chemical reaction, atoms are In a chemical reaction, atoms are rearranged, but they cannot be rearranged, but they cannot be destroyed or changed.destroyed or changed.

► If an atom appears on the left side of If an atom appears on the left side of the reaction, it must appear on the the reaction, it must appear on the right side.right side.



► In the reaction above, there are unequal In the reaction above, there are unequal numbers of atoms on either sidenumbers of atoms on either side Potassium (K): 2 atoms on the left, 1 atom Potassium (K): 2 atoms on the left, 1 atom

on the righton the right Oxygen (O): 2 total on the left, 1 atom on Oxygen (O): 2 total on the left, 1 atom on

the rightthe right Hydrogen (H): 2 atoms on the left, 1 atom Hydrogen (H): 2 atoms on the left, 1 atom

on the right.on the right.



►The reaction must be modified in order The reaction must be modified in order to make the atoms equalto make the atoms equal

►We CANNOT add subscripts to KOH, We CANNOT add subscripts to KOH, because that would change the because that would change the compound.compound.

► Instead, we add Instead, we add coefficients in frontcoefficients in front of compounds.of compounds.


Determine how many of each atom are Determine how many of each atom are present.present.

___ K___ K22O + ___ HO + ___ H22O O ___ KOH ___ KOH

K KO H HO K HO

K: 2K: 2 K: 1K: 1H: 2H: 2 H: 1H: 1O: 2O: 2 O: 1O: 1

Balancing an EquationBalancing an EquationThere are different numbers of atoms on There are different numbers of atoms on both sides. In order to match them up, both sides. In order to match them up, we can add more compounds, but not we can add more compounds, but not atoms alone.atoms alone.

___ K___ K22O + ___ HO + ___ H22O O ___ KOH ___ KOHK KO H HO K HO

K: 2K: 2 K: 1K: 1H: 2H: 2 H: 1H: 1O: 2O: 2 O: 1O: 1

K HO

Balancing an EquationBalancing an EquationThe number of each atom in the The number of each atom in the compound changes.compound changes.

___ K___ K22O + ___ HO + ___ H22O O ___ KOH ___ KOH

K KO H HO K HO

K: 2K: 2 K: 1K: 1H: 2H: 2 H: 1H: 1O: 2O: 2 O: 1O: 1

K HO222

Balancing an EquationBalancing an EquationNow that all the atoms are balanced, we Now that all the atoms are balanced, we can add up all the compounds.can add up all the compounds.

1 K1 K22O + 1 HO + 1 H22O O 2 KOH 2 KOH

K KO H HO K HO

K: 2K: 2 K: 1K: 1H: 2H: 2 H: 1H: 1O: 2O: 2 O: 1O: 1

K HO222

This is called a

coefficient

Balancing an EquationBalancing an EquationDetermine how many of each atom are Determine how many of each atom are present.present.

___ H___ H22 + ___ O + ___ O22 ___ H ___ H22OO

HH OO H HO

H: 2H: 2 H: 2H: 2O: 2O: 2 O: 1O: 1

Balancing an EquationBalancing an EquationThe hydrogen is okay, but the oxygen is The hydrogen is okay, but the oxygen is not. Add another Hnot. Add another H22O in order to O in order to balance the oxygen.balance the oxygen.

___ H___ H22 + ___ O + ___ O22 ___ H ___ H22OOHH OO H HO

H: 2H: 2 H: 2H: 2O: 2O: 2 O: 1O: 1

H HO

Balancing an EquationBalancing an EquationThe hydrogen is okay, but the oxygen is The hydrogen is okay, but the oxygen is not.not.

___ H___ H22 + ___ O + ___ O22 ___ H ___ H22OO

HH OO H HO

K: 2K: 2 K: 1K: 1H: 2H: 2 H: 1H: 1O: 2O: 2 O: 1O: 1

K HO222


___ Al + ___ FeO ___ Al + ___ FeO ___ Al ___ Al22OO33 + ___ Fe + ___ Fe

Al: 1Al: 1 Al: 2Al: 2

O: 1O: 1 O: 3O: 3

Fe: 1Fe: 1 Fe: 1Fe: 1


Begin balancing the aluminum by Begin balancing the aluminum by adding a 2adding a 2

__22_ Al + ___ FeO _ Al + ___ FeO ___ Al ___ Al22OO33 + ___ Fe + ___ Fe

Al: 1Al: 1 Al: 2Al: 2

O: 1O: 1 O: 3O: 3

Fe: 1Fe: 1 Fe: 1Fe: 1


Recount the aluminum atomsRecount the aluminum atoms

__22_ Al + ___ FeO _ Al + ___ FeO ___ Al ___ Al22OO33 + ___ Fe + ___ Fe

Al: 2Al: 2 Al: 2Al: 2

O: 1O: 1 O: 3O: 3

Fe: 1Fe: 1 Fe: 1Fe: 1


Move on to oxygen – Balance it by Move on to oxygen – Balance it by placing a 3 in front of FeO, and then placing a 3 in front of FeO, and then recount the atomsrecount the atoms

__22_ Al + __ Al + _33_ FeO _ FeO ___ Al ___ Al22OO33 + ___ Fe + ___ Fe

Al: 2Al: 2 Al: 2Al: 2

O: 3O: 3 O: 3O: 3

Fe: 3Fe: 3 Fe: 1Fe: 1


By adding the 3, we also changed the By adding the 3, we also changed the iron – this is the only way to balance, iron – this is the only way to balance, so we now fix the iron by adding so we now fix the iron by adding another coefficientanother coefficient

__22_ Al + __ Al + _33_ FeO _ FeO ___ Al ___ Al22OO33 + _ + _33_ Fe_ Fe

Al: 2Al: 2 Al: 2Al: 2

O: 3O: 3 O: 3O: 3

Fe: 3Fe: 3 Fe: 3Fe: 3


Now everything is balancedNow everything is balanced

__22_ Al + __ Al + _33_ FeO _ FeO ___ Al ___ Al22OO33 + _ + _33_ Fe_ Fe

Al: 2Al: 2 Al: 2Al: 2

O: 3O: 3 O: 3O: 3

Fe: 3Fe: 3 Fe: 3Fe: 3


Identify the number of each atom Identify the number of each atom present – Start with atoms in the fewest present – Start with atoms in the fewest compounds. We tend to keep H and O compounds. We tend to keep H and O last.last.

___ SiO___ SiO22 + ___ HF + ___ HF ___ SiF ___ SiF44 + ___ H + ___ H22OO

Si: 1Si: 1 Si: 1Si: 1

F: 1F: 1 F: 4F: 4

H: 1H: 1 H: 2H: 2

O: 2O: 2 O: 1O: 1


Silicon is done, so move on to fluorine.Silicon is done, so move on to fluorine.

___ SiO___ SiO22 + _ + _44_ HF _ HF ___ SiF ___ SiF44 + ___ H + ___ H22OO

Si: 1Si: 1 Si: 1Si: 1

F: 4F: 4 F: 4F: 4

H: 4H: 4 H: 2H: 2

O: 2O: 2 O: 1O: 1


Now move on to hydrogen. Since the Now move on to hydrogen. Since the compound has 2 hydrogen atoms in it, compound has 2 hydrogen atoms in it, we we multiplymultiply to get the correct number. to get the correct number.

___ SiO___ SiO22 + _ + _44_ HF _ HF ___ SiF ___ SiF44 + _ + _22_ H_ H22OO

Si: 1Si: 1 Si: 1Si: 1

F: 4F: 4 F: 4F: 4

H: 4H: 4 H: 4H: 4

O: 2O: 2 O: 2O: 2


Oxygen is already done. Everything is Oxygen is already done. Everything is balanced.balanced.

___ SiO___ SiO22 + _ + _44_ HF _ HF ___ SiF ___ SiF44 + _ + _22_ H_ H22OO

Si: 1Si: 1 Si: 1Si: 1

F: 4F: 4 F: 4F: 4

H: 4H: 4 H: 4H: 4

O: 2O: 2 O: 2O: 2

Writing Chemical Equations

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